1. Field of the Invention
The present invention relates to dye developing agents and particularly to novel dye developing agents utilized for photographic materials for a color diffusion transfer process.
2. Description of the Prior Art
Generally, dye developing agents are compounds which have a developing agent portion capable of developing silver halide and a dye portion and which can be diffused in photographic layers during development; they are fixed in portions of a photosensitive material in a color diffusion transfer process which correspond to exposed silver halide during development (after exposure) and retain their diffusibility in unexposed silver halide areas to give a transferred image on an image receiving element.
In a diffusion transfer image forming process, a photosensitive element comprising at least one silver halide emulsion layer is processed with a processing solution, e.g., immersion, coating, spraying, flowing, etc., after exposure, and is placed upon an image receiving element comprising a dye receiving layer to provide a dye diffusion transfer image thereon either before, after or during processing. In practice, the photosensitive element comprises at least one silver halide layer and a dye developing layer in combination with the silver halide layer, and a processing solution is uniformly coated therebetween when the photosensitive element is placed upon the image receiving element. The processing solution is commonly contained in a capsule which is ruptured to spread the processing solution between the stacked elements, i.e., the photosensitive element and the image receiving element.
A photosensitive material using a dye developing agent which has an absorption in the spectrally sensitized wavelength range of a silver halide emulsion which has been spectrally sensitized to red light, green light or blue light, together with a silver halide emulsion intrinsically having such spectral sensitivity, is practically designed so that the photographic transfer images can be viewed from the exposure side or from the reverse side. As means for combining such dye developing agents with such silver halide emulsions, there are, for example, (i) a method which comprises providing a silver halide photosensitive emulsion layer adjacent the exposure side of a hydrophilic colloid layer which contains a dye developing agent which has an absorption in a spectrally sensitized wavelength range of the silver halide emulsion, (ii) a method which comprises providing a hydrophilic colloid layer containing a dye developing agent which has an absorption in a spectrally sensitized wavelength range of the silver halide emulsion adjacent the exposure side of a silver photosensitive emulsion layer and (iii) a method which comprises using such a silver halide emulsion layer containing such a dye developing agent. However, in methods (ii) and (iii) the apparent sensitivity of the silver halide photosensitive emulsion is considerably decreased due to a filter effect caused by light absorption of the dye developing agent, which is conventionally used in large amounts.
To overcome such defects, U.S. Pat. No. 3,307,947 proposes the use of azotype magenta dye developing agents which have a spectral absorption peak in the short wavelength range before processing due to a hydroxyl group (auxochrome in the azotype magenta dye developing agent) being acylated, whereby apparent desensitization at exposure due to the filter effect is decreased while the long wavelength absorption required for image formation is recovered by development processing after exposure. Since the azotype magenta dye developing agent is of the temporary short wavelength absorption type (the hydroxyl group (auxochrome) being temporarily acylated), the bathochromic effect thereof is insufficient when it is changed into the temporary short wavelength absorption type, though it has the advantage that the acyl group is easily released during development to recover its color.
On the other hand, a dye developing agent having an amino group (an auxochrome having a sufficient bathochromic effect) is easily chemically changed into a short wavelength absorption type dye developing agent by conventional acylation. However, it has the serious defect that the color is not recovered at development because an amide bond is strong as compared with an ester bond. For example, U.S. Pat. No. 2,983,605 discloses that an aminoanthraquinone dye developing agent is changed into a short wavelength absorption type dye developing agent by benzoylation of the amino group, but such chemically altered dye developing agent does not recover its original color under development conditions.